This invention relates to a safety device for a plug door used in railroad box cars, and more particularly to a safety crank assembly that is mounted between the plug door and the retainer track above the door to prevent the plug door from falling off the car in case of failure of the normal operating crank assemblies.
Safety crank assemblies for plug doors have been known for some time and one embodiment thereof is described in U.S. Pat. No. 3,913,269 which issued on Oct. 21, 1975 for "Safety Cranks for Plug Doors". The described assembly includes a safety crank arm which has a horizontal center portion, and a downwardly and an upwardly extending end portion. The downwardly extending end portion is pivotally mounted to the door and the upwardly extending end portion is provided with a roller which engages the U-shaped channel in the retainer track.
While the safety crank assembly configuration described in U.S. Pat. No. 3,913,269 has been found fairly satisfactory, it is unable, for reasons explained hereinafter, to support over 9,000 pounds vertically and 5,000 pounds horizontally, these being the requirements set forth in a new set of regulations adopted by the Association of American Railroads.
One of the reasons that this prior art safety crank assembly is unable to meet these specifications, as will become better understood hereinafter, is due to the fact that in case of failure, the lower horizontal shelf of the retainer track must take the entire load of the plug door, and the load is exerted by the horizontal portion of the safety crank directly on the unsupported edge of the shelf. This exerts a very considerable bending moment on the shelf which causes it to bend and which makes it unable to comply with the new load specifications. Of course, it may be possible to strengthen the lower shelf by making it from a heavier gauge metal, say 1/4 inch or heavier instead of the present 3/16 inch or 1/4 inch, but this would require the retrofitting of many hundred thousands of railroad freight cars with new and heavier retainer tracks which is not economical. Also, and ignoring the new requirements of the Association of American Railroads, it is always desirable to have a safety crank assembly that provides a maximum margin of safety.